<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>welcome flask!</title>
</head>
<body style="display: flex">
    <div class="welcome">welcome flask!</div>
</body>
<style>
    .welcome{
        height: 60vh;
        width: 100%;
        font-weight: bold;
        font-size: 35PX;
        display: flex;
        justify-content: center;
        align-items: center;
    }
</style>
</html>